Lexus SC300 / Lexus SC400. Manual - part 925

OK

NG

OK

NG

OK

NG

NO

YES

3

Check for open and short in harness and connector between engine & ECT ECU and main oxy-

gen sensor, engine & ECT ECU and check connector (See page 

IN–27

).

Repair or replace harness or connector.

4

Check each item found to be a possible cause of problem.

Check each circuit found to be a possible cause of trouble according to the results of the check in 1 or
2.  The numbers in the table below show the order in which the checks should be preformed.

 

TR–132

 

TR–6

 

TR–51

 

TR–13

 

TR–114

 

TR–88

 

TR–68

 

TR–72

Repair or replace.

5

Check comparession (See page 

EM–30

).

Repair or replace.

6

Does malfunction disappear when a good main oxygen sensor is installed?

Replace main oxygen sensor.

check and replace engine & ECT ECU.

TR–79

–

ENGINE TROUBLESHOOTING

Circuit Inspection

OK

NG

OK

NG

NO

YES

7

Check each item found to be a possible cause of problem.

Check each ciruit found to be a possible cause of trouble according to the results of the check in 1. The
numbers in the table below show the order in the which the checks should be performed.

 

TR–132

 

TR–6

 

TR–51

 

TR–13

 

TR–114

 

TR–88

 

TR–68

 

TR–72

 

TR–72

Repair or replace.

8

Check compression (See page 

EM–30

).

Repair or replace.

9

Does malfunction disappear when a good main oxygen sensor is installed?

Replace main oxygen sensor.

Check and replace engine & ECT ECU.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–80

–MEMO–

TR–81

ENGINE TROUBLESHOOTING

Diag. Code 27

Sub–Oxygen Sensor Circuit (Only for
USA spec.)

CIRCUIT DESCRIPTION

The sub–oxygen sensor is installed on the exhaust pipe. Its construction and operation is the same
as the main oxygen sensor on page 

TR–60

.

Code No.

Diagnostic Code Detecting Condition

Trouble Area

(1) Open or short in heater circuit of sub–

oxygen sensor for 0.5 sec. or more.



Open or short in heater circuit of sub–oxy-
gen sensor.



Sub–oxygen sensor heater.



ECU

27

(2) Main oxygen sensor signal is 0.45 V or

more and sub–oxygen sensor signal is
0.45 V or less under conditions (a)  (c).

(2 trip detection logic) *

(a) Coolant temp.: 80

°

C (176

°

F)

or more.

(b) Engine speed: 1,500 rpm or more.
(c) Accel. pedal: Fully depressed for 2

sec. or more.



Open or short in sub–oxygen sensor cir-
cuit.



Sub–oxygen sensor



ECU

* : See page 

TR–25

.

TR–76

–

ENGINE TROUBLESHOOTING

Circuit Inspection